Method and installation for utilizing waste products, which contain hydrocarbons and iron oxide, particularly mill scale sludges and coal fines

ABSTRACT

The invention relates to an apparatus and a method for utilizing hydrocarbon-containing and iron-oxide-containing waste products, in particular rolling scale sludges, and fine coals, in a metallurgical plant, in which the waste product is mixed with the fine coal, and if appropriate with bituminous substances, and is then agglomerated, in particular cold-briquetted, and is then used to build up the fixed bed in a melter gasifier and is converted in the latter in a melting-gasification zone.

[0001] The invention relates to a method and an installation for utilizing hydrocarbon-containing and iron-containing, in particular iron-oxide-containing, waste products, in particular rolling scale sludges, and fine coals in or from a metallurgical plant. The invention also relates to a method for producing pig iron and/or primary steel products.

[0002] What is known as scale is produced during steel processing, in particular in the field of primary forming or deformation. In a rolling mill, this scale is referred to as rolling scale.

[0003] In the area of a rolling mill, the scale is contaminated by operating media, for example greases or oils, making it much more difficult to reuse these waste materials.

[0004] The prior art has disclosed various methods for reutilizing a rolling scale sludge, such as a mixture of scale, oil or grease, and water is generally known. In these methods, the rolling scale sludge, which is produced during the waste water treatment of the metallurgical plant, in particular in a rolling mill, is rendered useable by special methods and apparatus. In particular the hydrocarbons which are contained in the rolling scale sludge have proven problematic in this context, since off-gases which are harmful to health are formed during conventional thermal utilization of the rolling scale sludge, for example in a rotary tubular kiln. Procedures of this nature have proven uneconomical not least for this reason.

[0005] DE19755389A1 has taught a method for the pneumatic conveying and blowing of bulk material, in particular rolling scale, into a metallurgical smelting reactor, in particular into a melter gasifier. However, this publication scarcely takes any account of the process engineering consequences of the bulk material being introduced into a melter gasifier. Therefore, according to this teaching waste materials can only be utilized in a melter gasifier to a very limited extent.

[0006] EP0373577A1 teaches an apparatus and a method for treating clarification or industrial sludges which contain organic fractions. In the context of the conversion method which forms the teaching of this document, the sludges are subjected to preliminary mechanical dewatering, are conveyed into the interior of an indirectly heated continuous conveyor and are then exposed to heating, with simultaneous expulsion of the highly volatile components. In a subsequent second stage, they are held at a conversion temperature in order to expel the remainder of the volatile components from the solid product. In practice, this procedure has proven relatively inefficient, since it requires high process engineering and plant technology outlay.

[0007] DE19715839A1 deals with a method and an apparatus for cleaning oil-containing and water-containing rolling scale sludges in two method steps, in which the sludges are subjected to vacuum drying in the second method step. In practice, the installation has once again proven relatively inefficient, in particular entailing high set-up and operating costs.

[0008] DE3440037A1 teaches a method for the hot-briquetting of rolling scale sludges containing fat coal, followed by pyrometallurgical utilization. During the pyrometallurgical utilization of the rolling scale sludges in a blast furnace which forms the subject of the teaching of this document, high concentrations of off-gases which are harmful to health are produced. Furthermore, the method which forms the teaching of this document in practice has proven complex and cost-intensive. The formed coke produced using this method has poor metallurgical properties.

[0009] The present invention is therefore based on the object of overcoming the drawbacks of the prior art and developing a simple and economic method in accordance with the preamble of claim 1 and a suitable apparatus for carrying out the said method in accordance with claim 6.

[0010] This object is achieved, according to the method of the invention, by the characterizing clause of claim 1, and according to the apparatus of the invention by the characterizing clause of claim 6.

[0011] The term melter gasifier refers to a metallurgical appliance which is known from the prior art.

[0012] The present method of the invention has proven particularly suitable for the utilization of rolling scale sludges. In principle, however, it is possible to utilize all hydrocarbon-containing and iron-containing, in particular iron-oxide-containing, waste materials, for example oil-containing grinding sludges, using the method according to the invention.

[0013] A major objective of the present invention is to improve the thermomechanical and metallurgical properties of the carbon-containing charge materials, in particular of the relatively low-quality coals, preferably fine coals, which are used.

[0014] Where efforts made by the person skilled in the art were hitherto, as is extensively documented in the prior art, aimed mainly at removing as much of the hydrocarbons as possible from the rolling scale sludges as part of a pretreatment, the method according to the invention, for the first time, converts these sludges in their entirety in a melting-gasification zone in an economically particularly advantageous and simply way, in particular without the need for any complex pretreatment. Accordingly, both the carbon of the relatively low-quality coal, in particular of a fine coal, which may have a high tendency to swell, and also the iron oxide of the waste material are deliberately utilized to improve the iron and energy balance of an iron-producing process.

[0015] Compared to the utilization of waste materials in a blast furnace, the use of these materials in a melter gasifier is distinguished by the fact that the high temperatures in a melter gasifier lead to immediate decomposition of the hydrocarbon-containing components into the molecular basic constituents. At the high temperatures in a melter gasifier, in particular in a melting-gasification zone of a melter gasifier, substantially only CO and H₂ then exist. In the case of a shaft furnace, the stratified charging results in continuous heating of the charge material, which is in the form of a stock column, and therefore in condensing hydrocarbons evaporating off.

[0016] According to a preferred embodiment of the method according to the invention, the waste product has a hydrocarbon content of greater than 0.1% by weight, in particular of between 0.1 or 0.2% by weight and 2% by weight. The hydrocarbons are preferably greases or oils, for example rolling oils or rolling greases, which are distinguished by a high thermal stability. Hitherto, it was only possible for waste materials contaminated with such substances to be utilized to a limited extent or with considerable difficulty.

[0017] According to a preferred embodiment of the invention, the waste product predominantly comprises metallic iron, in particular at least 1% by weight of Fe, and iron oxides, in particular Fe₂O₃ and/or Fe₃O₄.

[0018] According to a preferred embodiment of the present invention, the charging of the agglomerates is performed by the force of gravity, for example in the dome region, preferably the upper dome region, of the melter gasifier, preferably above the fixed bed.

[0019] For operation of a melter gasifier, a solid carbon carrier, in particular a lumpy coal, with a good thermomechanical stability and a suitable grain size, in particular of greater than 8 mm, is required. A coal of this nature is not readily available and is correspondingly expensive or accompanied by fine unusable particles which, without suitable and complex pretreatment, would have an adverse effect on the melting process when used in a melter gasifier.

[0020] Hitherto, an agglomerated, in particular briquetted, fine coal could only be used to a limited extent as a fully equivalent replacement for coal in lump form in a melter gasifier. As tests have shown, the use of suitable waste materials, for example rolling scale sludges, in a method for producing agglomerated, in particular briquetted, carbon carriers from fine coal, significantly improves the thermal stability, in particular the thermomechanical properties, and/or the metallurgical properties of the agglomerates, and also damps the expansion characteristics of in particular highly volatile, possibly fresh, coals in the melter gasifier. It is therefore possible to widen the range of possible uses for briquetted fine coal using the method according to the invention. This leads to significant cost savings.

[0021] According to a preferred embodiment of the invention, the melter gasifier used is a melter gasifier which operates in accordance with the COREX method, which is known to the person skilled in the art. According to a particular embodiment of the invention, the melter gasifier is configured and operated, and in particular a fixed bed of a melter gasifier is built up, in accordance with the teaching disclosed by the published patent application AT16132000.

[0022] According to a further preferred embodiment of the invention, operation of the melter gasifier requires the use of a lumpy carbon carrier, in particular lumpy coal, to build up a fixed bed. This fixed bed, which allows gas to pass through, makes it possible to fully reduce the iron oxide, in particular in the form of fixed-bed reduction, and to drain the liquid, melted pig iron. The lumpy carbon carrier used for this purpose must in this respect have a sufficiently high thermomechanical stability and a suitable grain size. Furthermore, the carbon carrier used should have good metallurgical properties, in particular a good reactivity and/or the minimum possible tendency to swell.

[0023] According to a particular embodiment of the method according to the invention, the waste material which has been mixed with fine coal and agglomerated at least partially forms the lumpy carbon carrier required for operation of the melter gasifier. This makes it possible to utilize the fine coal which cannot be utilized directly in the process and may have been separated from the lumpy primary coal and therefore at the same time to at least partially dispense with the use of a lumpy primary coal which normally has to be bought in, resulting in considerable cost savings. By definition, the term primary coal refers to bought-in lumpy coal, which is virtually always accompanied by a fine coal as is formed, for example, during transport.

[0024] According to a particular embodiment, the agglomerate which has been produced, in terms of its volume, is based predominately on fine coal.

[0025] According to a particular embodiment of the invention, the iron-containing waste material is in finely distributed form in the fine coal, in particular following homogenization and/or agglomeration. According to a particular embodiment of the invention, therefore, the waste material is comminuted, in particular finely milled, before being mixed with the fine coal.

[0026] According to a particular embodiment of the invention, the storage properties of the agglomerates produced are improved, since the use of rolling scale sludges or corresponding waste materials makes it possible to use bitumen of higher softening points as binders, which in turn reduce the brittleness of the agglomerates, preferably in the cold season or at low temperatures.

[0027] According to a particular embodiment of the method according to the invention, the agglomeration step is a cold-briquetting step, which is carried out in particular at temperatures of below 100° C., preferably below 85° C. This form of agglomeration is distinguished by its particularly good economics.

[0028] According to one feature of the method according to the invention, the waste product is broken down into a carbon-containing, in particular hydrocarbon-containing, fraction and an iron-oxide-containing fraction in the melting-gasification zone, the carbon-containing, in particular hydrocarbon-containing, fraction being substantially converted into CO and H₂, and the iron-oxide-containing fraction being reduced and melted down. This means that the method has available to it reducing CO which can be used on the one hand in the melting-gasification zone itself and on the other hand, for example, for reduction of a metal-oxide-containing charge material in a reduction shaft furnace. The iron content of the agglomerates is fully reduced and melted down, thereby contributing to an increase in the iron yield in the melting-gasification zone.

[0029] The use of rolling scale can therefore be implemented as part of a closed circuit economy of a metallurgical plant. Moreover, the fine coal, which is preferably produced as a result of comminuting mechanisms while the lumpy coal is being transported and which has not hitherto been sufficiently taken into account in the prior art, contributes directly to the production of pig iron, thereby improving the economics of the method used for obtaining pig iron.

[0030] The direct utilization of the waste materials in a melting appliance as taught by the present invention for the first time makes it possible to achieve economic utilization of these materials.

[0031] According to a further feature of the method according to the invention, the binder and/or the waste product and/or the fine coal, as the main component of the agglomerate, is/are mixed with metallurgical dusts during the agglomeration and/or before the agglomeration.

[0032] Metallurgical dusts have hitherto been land-filled, at considerable cost. According to the invention, the addition of metallurgical dusts, for example to the waste material and/or the fine coal, optimizes the agglomeration and achieves an economic benefit from the complete utilization of the metallurgical dusts. The addition of the metallurgical dusts in particular improves the strength and storage properties of the agglomerates.

[0033] According to a further feature of the invention, the waste product is dewatered to a residual moisture content of less than 15% by weight, in particular to a residual moisture content of less than 10% by weight, preferably by means of a filter press and/or centrifuge, prior to the agglomeration. The agglomerates produced in this way are distinguished by a high strength and good storage properties.

[0034] According to a further embodiment, the invention relates to a method for producing pig iron and/or primary steel products by means of a melting-gasification zone, in which an iron-containing charge material is melted, while a carbon carrier and oxygen-containing gas are being supplied, and the carbon carrier is formed at least in part from a hydrocarbon-containing and iron-oxide-containing waste material, in particular a rolling scale sludge. The advantages which have already been listed above with regard to the utilization of the waste material, in particular the rolling scale sludge, apply to these methods too.

[0035] According to a particular embodiment of the method according to the invention, the waste material, before being used in the melting-gasification zone, is mixed as a mixing component, with a predetermined quantity of the fine coal which is to be agglomerated, and if appropriate bituminous substances, and then agglomeration is carried out.

[0036] According to a further embodiment of the method according to the invention, to produce pig iron, the iron-containing charge material, before being introduced into the melting-gasification zone, is at least partially reduced, for example is reduced from hematite and/or magnetite to iron sponge, in a reduction zone, for example in a reduction shaft furnace which is preferably designed as a prereduction zone. According to a preferred embodiment of the invention, the subsequent full reduction and/or melting of the iron-containing charge material for the production of pig iron takes place in the melter gasifier.

[0037] According to a further feature of the method according to the invention, a CO and H₂-containing gas is generated from the carbon carrier in the melting-gasification zone, is extracted at the melting-gasification zone and is introduced as reduction gas into the reduction zone, for example into the reduction shaft furnace.

[0038] To operate a melter gasifier, according to a preferred embodiment a carbon carrier in lump form with good thermal, thermomechanical and metallurgical properties, in particular a high thermal stability, is required. The grain size of the carbon carrier should in this case be at least 8 mm.

[0039] To enable fine coal, undersized coal material from screening operations and coal in dust form to be used, according to the prior art it is customary for these charge materials to be agglomerated. The cold-briquetting of coal with binders is a method which is known from the literature and from practice. For use in a melter gasifier of the type described in the introduction, it is preferable for the fine coal-containing charge materials to be agglomerated by the use of bitumen as a binder.

[0040] Although bitumen is available throughout the world, it is subject to the fluctuations of the market price for crude oil.

[0041] For this reason, according to the invention it is proposed to mix bitumen with a fine scale and to use this mixture as a binder for the production of the agglomerates from fine-grained carbon carriers.

[0042] These measures result in the following advantages:

[0043] Saving on bitumen on account of the partial replacement with fine rolling scale sludge

[0044] Good wettability of the bitumen with the oil fraction of the rolling scale sludge

[0045] An increase in the thermomechanical stability of the agglomerates on account of the ultrafine inert material, in particular on account of the preferably finely distributed waste material in the coke skeleton, which damps the expansion properties of the highly volatile coal agglomerated in this way in the melter gasifier.

[0046] Use of bitumen with a higher softening point becomes possible on account of the addition of oil-containing fine scale mixture.

[0047] Improved storage properties of the agglomerates produced, since the brittleness of agglomerates, in particular in the cold season or at low temperatures, is reduced when using bitumen with an increased softening point with the addition of fine rolling scale sludge.

[0048] The economic advantages can be summarized as follows:

[0049] Oil-containing scale, which is produced as a problematic waste material in metallurgical plants and usually has to be disposed of (landfill), can advantageously be reused, making optimum use of its constituents, as part of a circuit economy. The oil content of the scale makes it possible to reduce the proportion of bitumen and can also be utilized for energy purposes in the melter gasifier. Furthermore, the iron content of the rolling scale sludge is utilized quantitatively on account of its use in a melter gasifier using the method described above for the production of pig iron.

[0050] A typical, though non-restricting, composition of a rolling scale used is as follows: Metallized iron: approx. 1% by weight Iron Fe₃O₃: approx. 56% by weight Iron Fe₂O₄: approx. 38% by weight Carbon: approx. 2% by weight Silicon: approx. 2% by weight Residual oxides: approx. 1% by weight

[0051] Rolling scale sludges are generally characterized by hydrocarbon contents of over 0.1% by weight, in particular of over 0.2% by weight, making it difficult to utilize these waste materials for example in a sintering process or in a blast furnace. Depending on their origin, rolling scale sludges may also have hydrocarbon contents of over 0.5-1% by weight or even of over 2-3% by weight, meaning that the proposed method for utilizing waste materials of this type has proven extraordinarily favorable. In principle, it can be assumed that as the hydrocarbon content rises, a pretreatment which corresponds to the prior art will entail increasing costs, and consequently the inventive method of utilization proves particularly economical.

[0052] The rolling scale sludge should if possible have only a small proportion of elements which, according to the knowledge of the person skilled in the art, have an adverse effect on the quality of the pig iron which is produced, and the sludge is correspondingly pretreated if necessary. For example, a high content of heavy metals or a high sulfur content would lead to significant quality losses.

[0053] According to a particular embodiment, the composition of the agglomerates intended for use in the melter gasifier is substantially as follows:

[0054] Ultrafine coal (grain size<1 mm)—approx. 40-70% by weight or 90 to 95% by volume—and

[0055] Rolling scale sludge (dewatered)—approx. 30-50% by weight or 5 to 10% by volume—, and in addition

[0056] Metallurgical dusts (minor quantities, must not be contaminated)—approx. 10-15% by weight—

[0057] Binder: approx. 2-5% by weight of bitumen or bitumen emulsion.

[0058] The size of the agglomerates is preferably a diameter of between 10 and 40 mm.

[0059] Metallurgical dusts as components of the agglomerate in principle play a subordinate role. In conventional metallurgical plants, dusts are usually highly contaminated and are therefore relatively unsuitable for recycling into a pig iron stage, such as for example in a melter gasifier.

[0060] Uncontaminated dusts of all kinds (oxidic, C-containing), as are produced, for example, in a direct reduction shaft furnace, on the other hand, can, taking into account economic considerations, be agglomerated, for example granulated, using the method which forms the teaching of the invention and recycled into the pig iron stage.

[0061] The invention is also characterized by an apparatus for utilizing a hydrocarbon-containing and iron-oxide-containing waste product, in particular a rolling scale sludge, in a metallurgical plant, in which an agglomeration installation for producing agglomerates from a, preferably homogenized, mixture of a hydrocarbon-containing and iron-oxide-containing waste material with a fine coal and if appropriate with a bituminous material, and also a melter gasifier for utilizing the agglomerates are provided.

[0062] According to an additional feature of the invention, a homogenization apparatus, in which the waste material, in particular the rolling scale sludge, and the fine coal and if appropriate a bituminous material are introduced via metering devices and homogenization is carried out before the homogenized mixture is fed to the agglomeration installation and ultimately, in agglomerated form, to the melter gasifier, is provided at the agglomeration installation. According to further embodiments of the apparatus according to the invention, hopper systems in which the charge material can be temporarily stored are provided at the corresponding apparatus.

[0063] According to a particular embodiment of the apparatus according to the invention, at least one vessel and/or at least one metering device for the storage and/or metered addition of the fine coal and/or the waste material and/or other charge materials, in particular of metallurgical dusts and/or binder, is provided at the agglomeration installation and/or the homogenization installation. 

1. A method for utilizing hydrocarbon-containing and iron-oxide-containing waste products, in particular rolling scale sludges, and fine coals, preferably in a metallurgical plant, particularly preferably for producing pig iron and/or primary steel products, in which the waste product is mixed with the fine coal, and mixed with bituminous substances, and is then agglomerated, in particular cold-briquetted, and is then used to build up a fixed bed in a melter gasifier and is converted in the latter in a melting-gasification zone.
 2. The method as claimed in claim 1, characterized in that the waste product has a hydrocarbon content of greater than 0.1% by weight, in particular of greater than 0.2% by weight.
 3. The method as claimed in claim 1 or 2, characterized in that the waste product is broken down into a carbon-containing fraction and an iron-oxide-containing fraction in the melting-gasification zone, the carbon-containing fraction being converted substantially into CO and H₂ and the iron-containing fraction being reduced and melted down.
 4. The method as claimed in one or more of claims 1 to 3, characterized in that the fine coal and/or the waste product is/are mixed with metallurgical dusts during the agglomeration and/or prior to the agglomeration.
 5. The method as claimed in one or more of claims 1 or 4, characterized in that the waste product is dewatered to less than 10% by weight of residual moisture, preferably by means of a filter press and/or centrifuge, prior to the agglomeration. 